1. Field of the Invention
The present invention relates to a motor-driven steering assist apparatus.
2. Description of the Related Art
In a motor-driven steering assist apparatus of a rough road traveling vehicle, such as a buggy vehicle or the like, as described in Japanese Patent Application Laid-open No. 2004-336565 (patent document 1), there is a structure which is interposed between a steering wheel and a tire wheel side steering member, which assists steering force applied to the steering wheel by a driver on the basis of torque generated by an electric motor.
In the motor-driven steering assist apparatus in the patent document 1, a single unit body covered by first to third housings has an input shaft to which a steering wheel is connected and an output shaft to which a wheel side steering member is connected. A torque sensor is provided between the input shaft and the output shaft. An electric motor is driven in correspondence to a detected torque of the torque sensor. A worm gear is coupled to a rotary shaft of the electric motor, and a worm wheel is coupled to the output shaft and is engaged with the worm gear built-in. Further, an upper end portion of the input shaft and the torque sensor are supported to the first housing. An upper end portion of the output shaft, the electric motor, the worm gear and the worm wheel are supported to the second housing. A lower end portion of the output shaft is supported to the third housing, and the second housing can be attached to a vehicle body frame (a vehicle body side bracket).
In the motor-driven steering assist apparatus in the patent document 1, an attaching boss is provided at a plurality of positions in a peripheral direction of an outer periphery of the second housing, and an attaching bolt inserted and attached to the attaching boss is fastened to a vehicle body side attaching bracket. The second housing receives the worm gear and the worm wheel and forms a large outer diameter itself. The attaching boss provided in the outer periphery of the second housing protrudes more to an outer side, the vehicle body side bracket is enlarged in size, and it is hard to avoid an interference with peripheral equipment such as an engine or the like. Further, the second housing receives the worm gear and forms a different outer shape, and complicated consideration is necessary for arranging the attaching boss while avoiding the worm gear receiving portion.
Further, in the motor-driven steering assist apparatus in the patent document 1, it is necessary that the attaching boss is provided at a plurality of positions, for example, three positions in the peripheral direction of the outer periphery of the second housing. Three attaching bolts inserted and attached to the attaching boss are fastened, so that it is necessary to carry out a complicated procedure.